Suicide bombers first attacked Uzbekistan in March

The State Department has warned Americans travelling or living in Uzbekistan to be especially vigilant.

There have been a number of violent attacks in Uzbekistan, including suicide bombings at the US and Israeli embassies.

The Uzbek authorities have blamed the attacks on groups linked to al-Qaeda.

"The embassy urges Americans in Uzbekistan to exercise extreme caution, including avoiding large crowds, celebrations and public places where Westerners generally congregate," the State Department said in a statement on Wednesday.

It gave no further details on what kind of attacks might be planned.

Troops base

Hundreds of US troops are currently stationed in Uzbekistan, which is on the border with Afghanistan.

The country became a key regional ally to the US in the wake of the September 11 attacks, when American troops used military bases there.

A series of violent attacks by alleged Islamist militants have shocked Uzbekistan in recent months.

On 30 July, suicide bombers targeted the Israeli and US embassies in Tashkent, and the prosecutor general's office.

Three people were killed in the attacks.

More than 40 people also died during a series of violent incidents in late March and early April.